OLYMPIA — Eastern Washington dairies will be needlessly delayed as they fertilize spring crops with manure under a Department of Ecology rule meant to protect groundwater, the Washington State Dairy Federation claims in a lawsuit filed last week in Thurston County.

The rule imposes statewide a formula that prohibits spreading manure until temperatures are above freezing for a prolonged period. The formula, named T-Sum 200, will work in Western Washington's milder climate, but will prevent fertilizing in Eastern Washington's colder climate until mid-March in some cases, according to the federation.

The delay will deprive budding crops of nutrients without any benefit to water quality, the federation asserts. "T-Sum 200 is a meat cleaver and simply doesn't work in a climate like Eastern Washington," dairy federation Executive Director Dan Wood said. "You could have a warm week and still not clear the T-Sum level."

Ecology imposed the rule last year in the terms of permits for dairies and other confined animal feeding operations. The permits dictate how livestock operators must store and apply manure. The rules are a new layer of regulation for dairies, which already must follow a separate manure-management law enforced by the state Department of Agriculture.

The Pollution Control Hearings Board this year upheld most of Ecology's rules. Environmental groups have filed a separate lawsuit in Thurston County Superior Court alleging a half dozen deficiencies in the rules.

The dairy federation, joined by the Washington Farm Bureau, has one complaint — the application of T-Sum 200 east of the Cascades.

T-Sum 200 is reached when the sum of each day's mean temperature after Jan. 1 exceeds 200 degrees Celsius. The guide to when plants are ready to take up nitrogen was developed in the Netherlands and United Kingdom.

The dairy federation says Western Washington's climate is similar and T-Sum 200 would be reached in early February. Eastern Washington is far colder and drier, and the federation says Ecology should base the timing of manure spreading there on factors such as weather forecasts, soil conditions and the proximity of the water table.

The federation says Ecology hasn't provided a scientific reason for extending T-Sum 200 east of the Cascades.

In adopting T-Sum 200 statewide, Ecology noted that some commenters, including the dairy federation, thought the agency's earlier proposal to wait for "spring green up" before applying manure was too vague. Some commenters said T-Sum 200 was a common industry standard, according to Ecology.

The dairy federation maintains that Ecology wrongly interpreted its comments to justify imposing T-Sum 200 as a statewide threshold.

An Ecology spokeswoman said in an email that the agency "used the best available science and broad stakeholder input to develop a permit that is clear, practical and understandable."

"T-Sum 200 is a well-recognized method for determining the start date for land application and was suggested by commenters for use. We did not receive any method suggestions specific to Eastern Washington," she wrote.

Environmental groups allege the permits won't adequately monitor the discharge of pollutants into water and whether the pollutants are a risk to public health.

The environmental groups involved in the lawsuit are the Puget Soundkeeper Alliance, Community Association for Restoration of the Environment, Friends of Toppenish Creek, Sierra Club, Waterkeeper Alliance and Center for Food Safety.